Combustion cycles on four-stroke internal combustion engines can be modified to achieve various desired results such as improved fuel economy. In one method, the expansion stroke is increased relative to the compression stroke. The effect is sometimes referred to as a Miller Cycle or as an Atkinson Cycle. The Miller and Atkinson Cycles can be achieved by either closing the intake valve earlier than a normal or Otto Cycle (“Base”) with a shorter than normal intake valve lift duration (“EIVC”), or by closing the intake valve later by a longer than normal intake valve lift profile (“LIVC”).
Recent automotive and truck industry trends have placed increased importance on the reduction of fuel consumption and emissions of the internal combustion engine. One method of reducing fuel consumption is to optimize air intake and exhaust into the cylinders through incorporation of discrete valve profiles. Various systems have been developed for altering the valve-lift characteristics for internal combustion engines. Such systems, commonly known as variable valve timing (VVT) or variable valve actuation (WA), improve fuel economy, reduce emissions and improve drive comfort over a range of speeds.
Current axial cam shifting systems are limited to two discrete positions and thus two discrete valve lift profiles offering two valve lift functions. A two position system allows a simple actuation system that only needs to translate the axial shifting components to either a front or a rear position. Mechanical stops can be designed into the system to stop the components in the correct positions for positive axial location. While the current systems are satisfactory for their intended purpose it is desirable to provide more than two discrete valve lift profiles to further optimize the valve system for a given application and operating condition.